Method for producing artificial powder graphite

ABSTRACT

The invention relates to a method for obtaining artificial graphite powder for electrical engineering, manufacturing synthetic diamonds and in other fields of technology with especially high requirements for graphite purity. The novelty of the inventive method is the use of pyrolytic carbon material obtained by methane pyrolysis at a temperature of 2100-2400° C. Pyrolytic carbon obtained as a waste product of pyrolytic anisotropic material can be used as a carbon material. The method includes grinding carbon material and its graphitizing at a temperature of 2600° C.-2700° C. The inventive method simplifies the process of preparing artificial graphite powder and enhances the degree of graphitization, which improves the quality of the final product.

FIELD OF THE INVENTION

[0001] This invention relates to the production of artificial graphitepowders for electrical engineering, manufacturing synthetic diamonds andother applications that require a high degree of graphite purity.

BACKGROUND OF THE INVENTION

[0002] There is a known method of obtaining graphite powder, comprisingthe steps of grinding graphite material and its subsequent purification.Primary graphite formed in a blast furnace (Accepted Patent Applicationof Japan No. 6102528, published on Dec. 14, 1994), or graphite with adegree of purity below 95% (Accepted Patent Application of Japan No.6102529, published on Dec. 14, 1994.) are used as graphite sourcematerial. Graphite material is ground under the action of instantunidirectional external forces either in a jet mill or in a crusher withhigh-speed blades. Graphite material is purified with hydrofluoric acid(Accepted Patent Application of Japan No. 6102529, published on Dec. 14,1994), or with gaseous halogen at a high temperature (Accepted PatentApplication of Japan No. 6045446, published on Jun. 15, 1994), orconcentrated sulfuric acid (Accepted Patent Application of Japan No.7014803, published on Feb. 22, 1995.).

[0003] The well-known method of obtaining graphite powder is complicatedbecause of the hardware used. Low microhardness of graphite materialrequires the application of complex special devices and technologies forits grinding, and the use of highly corrosive media for graphitepurification requires special chemical-proof equipment. The method ofobtaining artificial graphite powder, including grinding carbon materialand its graphitizing at a temperature of 2600-2700° C. (Accepted PatentApplication of Japan No. 6021018, published on Mar. 23, 1994) is alsoknown. Fresh coke is used as a source of carbon, with a hydrogen contentof no less than 2%, or mixed with a carbonaceous substance in mesophase,which are treated after grinding with sulfuric or nitric acid, thenwashed with water, alkali or an organic solvent.

[0004] Artificial graphite powder obtained by well-known method ischaracterized by a modest degree of graphitization, i.e., degree ofapproximation of its structure to the perfect graphite structure, whichis the reason for obtaining graphite of insufficient quality. This isattributable to the fact that when fine-grinding the above source carbonmaterials, the elements of crystal structure are destroyed, i.e.,amorphization occurs. Hence, the graphitizing ability of initial carbonmaterials is reduced, resulting in obtaining artificial graphite ofmodest quality, whose structure is far from perfect graphite structure.The defects in the structure of artificial graphite powder obtained bythe well-known methods are also caused by residual impurities present incoke. In addition, the well-known method is complex because of hardwareused, as it requires special equipment resistant to the attack of strongacids and alkalis.

OBJECT AND SUMMARY OF THE INVENTION

[0005] The object of the proposed invention is to improve the method forthe production of artificial graphite powder, which ensures theenhancement of the degree of graphitization of the final product by theuse of a new substance and improves its quality with simultaneoussimplification of the method.

[0006] For achieving the above goal, in the well-known method ofobtaining artificial graphite powder, comprising the grinding of carbonmaterial and its graphitizing at a temperature of 2600-2700° C., thenovelty, according to the invention, is that pyrolytic carbon obtainedby methane pyrolysis at a temperature of 2100-2400° C. is used as carbonmaterial.

[0007] The other novelty is that waste product of pyrolytic anisotropicmaterial is used as carbon material.

[0008] Between the combination of essential features of the supposedinvention and achievable technical result, the following cause-effectrelation exists.

[0009] The application of pyrolytic carbon as carbon source material,obtained by methane pyrolysis at a temperature of 2100-2400° C., alongwith known features of the invention, provides the enhancement of degreeof graphitization of the final product, i.e., the degree ofapproximation of the structure of the obtained artificial graphitepowder to the perfect graphite structure. The structure of the pyrolyticcarbon was formed from graphite grids located parallel to the depositionsurface. Some of the parallel-located grids are combined incrystallites, thus ensuring pronounced anisotropy of pyrolytic carbon.

[0010] In the structure of pyrolytic carbon obtained by methanepyrolysis at a temperature of 2100-2400° C., large areas ofthree-dimensional array characteristic of graphite are noted. The moreperfect structure of initial carbon material causes the enhancement ofdegree of graphitization of artificial graphite obtained. In this case,the structure of pyrolytic carbon is characterized by high density,absence of macro- and transition pores and the presence only ofmicroporosities between crystallites. Structure imperfection between thelayers reflects the presence of significant internal pressure, which ischaracteristic of high anisotropy of thermal expansion of pyrolyticcarbon. This causes brittleness of pyrolytic carbon and its goodgrindability. When grinding pyrolytic carbon, the destruction occurspredominantly along cracks, defects and thin interpore walls, notdestroying the elements of crystal structure. Thus, grinding ofpyrolytic carbon obtained at the stated temperatures of 2100-2400° C.,does not worsen its graphitizing ability, thereby resulting inartificial graphite powder with practically perfect crystal graphitestructure. This is also conditioned by high purity of pyrolytic carbon,the initial carbon material. The absence of impurities in it is thereason for the absence of defects in the structure of graphite obtainedfrom pyrolytic carbon, which also raises the degree of itsgraphitization.

[0011] Good grindability of pyrolytic carbon due to its mechanicalproperties (brittleness, better microhardness in comparison withgraphite) allows the use of simple devices (ball mills, jaw crushers,etc.) for its grinding, while the high purity of pyrolytic carbonobviates the necessity for purification with highly corrosive agents,thus also simplifying the method. The use of pyrolytic carbon obtainedby methane pyrolysis at a temperature lower than 2100° C., as a carbonmaterial results in lowering the degree of graphitization of theartificial graphite powder obtained, due to less perfect crystalstructure of such pyrolytic carbon. The increase in the temperature ofmethane pyrolysis ensures better crystal structure of pyrolytic carbonobtained. However, the use of pyrolytic carbon obtained at a temperaturehigher than 2400° C. for the production of graphite powder isinexpedient, as it causes difficulties associated with grinding of suchpyrolytic carbon owing to lower microhardness and its adhering to therubbing surfaces requires the use of special devices and processes forgrinding. The subsequent graphitization at a temperature of 2600-2700°C. of ground pyrolytic carbon obtained by methane pyrolysis at thestated temperature of 2100-2400° C., owing to stresses arising in it(the compression stress is in a radial direction and the tension stressis in a tangential direction) and plastic flowability, causes change inthe orientation of crystallites and provides better texturing of thematerial, i.e., improves crystal structure of graphitized material.

[0012] The indicated temperature of graphitization is necessary andsufficient for transforming the structure of the ground pyrolytic carbonobtained by methane pyrolysis at a temperature of 2100-2400° C., intopractically perfect crystal graphite structure.

[0013] The use of a waste product of the process for the manufacture ofarticles from pyrolytic anisotropic material as a carbon source materialalso ensures better graphitization of artificial graphite powderobtained. The products from pyrolytic anisotropic material as blanks offlat shape and bodies of rotation are obtained by methane pyrolysis at2100-2400° C. and deposition of pyrolytic carbon on a special substrateof the specified shape. Simultaneously, pyrolytic carbon is deposited onother surfaces of the reactor, in which methane is pyrolyzed. Just thispyrolytic carbon is a waste product from pyrolytic anisotropic materialand at the present time it is not used anywhere.

[0014] Owing to the use of the above waste as carbon material, thesimultaneous enhancement of the graphitization degree of powderartificial graphite obtained and essential reduction of its cost areprovided.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0015] For realizing the proposed method, pyrolytic carbon obtained bymethane pyrolysis at a temperature of 2100-2400° C. in the reactor of anelectrical vacuum furnace (p 3-8 mm Hg) is used as carbon material withmethane supply at a rate of 50-150 l/min, depending on the volume of thereactor and the rate of pyrolytic carbon deposition (0.2-0.25 mm/hour).Thickness of the pyrolytic carbon layer is 5 to 10 mm, density is notless than 2.0 g/cm³. Then pyrolytic carbon is ground in a ball mill to20-90 μm. The obtained powder is subjected to graphitization at atemperature of 2600-2700° C. according to the well-known technology.

[0016] Waste product from pyrolytic anisotropic material (for example,

IIB-1,

IIA-3 grades) is also used as carbon material.

[0017] Waste product is pyrolytic carbon deposited on the inner surfacesof the electrical vacuum furnace reactor during the process of obtainingproducts as blanks of flat shape and bodies of rotation by pyroliticdeposition of pyrolitic carbon on special substrates of specified shapeby methane decomposition at 2100-2400° C.

[0018] The product obtained after graphitizing ground pyrolytic carbonis a high-purity artificial graphite powder with practically perfectgraphite structure of a particle size of 10-70 μm, which can be used inmanufacturing synthetic diamonds, in electrical engineering and in othertechnologies with especially high requirements of graphite purity.

[0019] Operation

[0020] The proposed method was tested on the operating equipment. Thegraphitization degree of artificial graphite powder obtained by theproposed method, has been determined by x-ray structural analysismethod. The degree of graphitization, i.e., the value showing the degreeof approximation of the structure of obtained artificial graphite powderto the perfect graphite structure is 0.98-0.99.

What is claimed is:
 1. The method of obtaining powder artificialgraphite including grinding of carbon material and its graphitizing at atemperature of 2600-2700° C., different in that pyrolytic carbonobtained by methane pyrolysis at a temperature of 2100-2400° C. is usedas carbon material.
 2. The method of obtaining powder artificialgraphite according to item 1, different in that waste product of theprocess for the manufacture of articles from pyrolytic anisotropicmaterial is used as carbon material.